As surgical techniques continue to progress and become less invasive, an increasing number of medical procedures are performed with the aid of a catheter. In general, a catheter is a flexible tube that is inserted into narrow openings within the body and is used to deliver and/or remove fluids or substances. An example of a medical procedure that utilizes a catheter is percutaneous transluminal coronary angioplasty (PTCA).
PTCA is a catheter-based technique whereby a balloon catheter is inserted into the blocked or narrowed coronary lumen of a patient. Once the balloon is positioned at the target site, the balloon is inflated causing dilation of the lumen. The balloon is deflated and the catheter is then removed from the target site thereby allowing blood to freely flow through the unrestricted lumen.
Although PTCA procedures aid in alleviating intraluminal constrictions, such constrictions or blockages reoccur in many cases. The cause of these recurring obstructions, termed restenosis, is due to the body's immune system responding to the trauma of the surgical procedure. As a result, drug therapies are often applied in combination with the PTCA procedure to avoid or mitigate the effects of restenosis at the surgical site. The drugs are delivered to the site via a needle housed within the catheter. The term “drug(s),” as used herein, refers to all therapeutic agents, diagnostic agents/reagents and other similar chemical/biological agents, including combinations thereof, used to treat and/or diagnose restenosis, thrombosis and related conditions.
Other procedures, such as those developed to control the effects and occurrence of angiogenesis, also utilize a catheter having a drug delivery needle. Angiogenesis is a process whereby new blood vessels are grown in the body for healing wounds and for restoring blood flow to tissues after injury or trauma. Angiogenesis occurs naturally in the body, both in normal states and in disease states. For example, in females, angiogenesis occurs during the monthly reproductive cycle to rebuild the uterus lining and to mature the egg during ovulation. In addition, angiogenic growth factors are also present during pregnancy to build the placenta and create the vessels necessary for circulation between the mother and fetus.
Angiogenesis also occurs in various disease states, such as cancer, diabetic blindness, age-related macular degeneration, rheumatoid arthritis, coronary artery disease, stroke, and other disorders. In cases of excessive angiogenesis, the new blood vessels feed diseased tissues, destroy normal tissues and, with respect to cancer, allow tumor cells to escape into the circulation and lodge in other organs. Conversely, insufficient angiogenesis causes inadequate blood vessel growth thereby impeding circulation which, in turn, potentially leads to tissue death.
Although angiogenesis occurs naturally in the body, various procedures have been developed to artificially control the occurrence and effects of angiogenesis. One such procedure is Percutaneous TransMyocardial Revascularization (PTMR). PTMR utilizes a laser catheter to create small channels in the diseased tissue. The channels re-establish direct blood flow to the tissue and allow oxygen-rich blood to saturate the oxygen-starved tissue. PTMR is generally used for the treatment of severe, end-stage coronary disease.
Another catheter-based procedure used to promote angiogenesis involves gene therapy. For this procedure, genetic material is delivered directly to the diseased area of the body via a catheter. In particular, genetic material, such as Vascular Endothelial Growth Factor (VEGF), is incorporated into gene delivery vehicles called vectors, which encapsulate therapeutic genes for delivery to the diseased cells. Many of the vectors currently in use are based on attenuated or modified versions of viruses. The vectors may also be synthetic versions in which complexes of DNA, proteins, or lipids are formed into particles capable of efficiently transferring genetic material. A needle injection catheter is used to deliver the vectors containing the genetic material to the appropriate cells of the patient in a safe and efficient manner.
These and other similar catheter-based procedures require accurate tracking of needle location as the catheter and needle are maneuvered through the system to the target site in the patient. Conventional catheter-based needle drug delivery devices utilize fluoroscopic imaging methods to track catheter and needle movement in the body of a patient. In general, a radiopaque coating is applied in a thin, dense layer on a portion of the catheter and/or needle that is then viewed utilizing a fluoroscope. However, this method is limited to visualizing device placement within the artery. This is a limitation when the target for the needle-born drug/therapy is outside the delivery vessel. Further, this method produces a planar (two-dimensional image) which may not be sufficient to accurately steer or track the location of the catheter through the body of the patient. In addition, due to inadequate fluoroscopic imaging resolution and limited mass/density of radiopaque material, these devices are also limited in their effectiveness to accurately position the catheter needle at the desired target site.